About 5 times faster at the moment.
It's true!
Though, according to my speed test (New 3DS XL, 200x240px, radius 5), QBLUR is 3x the speed of GBLUR. However, correcting for the fact that GBLUR only renders a quarter of the pixels in the end (half width and half height), more accurately, QBLUR is 12x the speed of GBLUR.
Nice job!
Is there any way to make it in full screen and dual screen?
Well, if you mean with XSCREEN, then yes you can.